The major WGA-binding glycoprotein was isolated from the spent culture medium of B16-F10 mouse melanoma cells. A molecular weight of 48,000 was estimated by SDS polyacrylamide gel electrophoresis. Serine and threonine comprised 25% of the total amino acid residues of the glycoprotein. The glycoprotein resembles glycophorin in that it contains both N-\and O-linked oligosaccharides, and the O-linked units appear to be in tetrasaccharide structures and clustered on the peptide backbone. Neuraminidase treatment released approximately 80% of the glycoprotein's sialic acid content, and the desialylated species was bound ricin-Sepharose. The interactions of fibronectin with unfractionated histones and histone subfractions (H1, H2A + H3, H2B, and H4) were studied under physiological conditions by laser nephelometry. It was found that fibronectin interacted preferentially with histone H2A + H3. Due to self-aggregation, fibronectin showed a very low relative light scattering. Eleven mouse monoclonal antibodies directed against epitopes on CNBr-peptides of the major sialoglycoconjugate of the human red blood cell, glycophorin A, were produced by hybridomas derived from P3-X63-Ag8.563 myeloma cells and spleen cells from BALB/c mice immunized with purified glycophorin. The monoclonal antibodies could be divided into four groups according to their reactivities with CNBr peptides in a direct ELISA assay: (1)\one antibody (6B5) that binds solely to the aminoterminal octapeptide (CNBr3); (2)\two antibodies (8F10 and 9C3) that bind to CNBr1 (residues 9-80); (3)\two antibodies (3D2 and 4C6) that are reactive with CNBr2, the C-terminal portion of the molecule (residues 81-131); and (4)\six antibodies which are cross-reactive with an epitope on both CNBr1 and CNBr3 glycopeptides. This cross-reactive epitope(s) appears to involve both carbohydrate and protein residues. (A)